The project Karpatian Tectonics Slovakia addresses the development of a coherent tectonic model for the Early Miocene in the Vienna Basin and adjacent areas. Studies include 2D/3D seismic interpretation in the Vienna Basin and structural fieldwork in the Outer West Carpathians. Structural data comprises 105 outcrops from the NW-rim of the Pieniny Klippen Belt (PKB) and Outer West Carpathian Flysch units in Northwest Slovakia and Eastern Czech Republic.
Structural data from the Outer West Carpathian Flysch Units (Biele Karpaty-, Magura-, Silesian Unit) depict (N)NW-directed shortening (DF1), which is related to the large scale architecture of the ENE-striking fold-and-thrust-belt. Thrust ages, obtained from the ages of youngest overthrust sediments indicate Eocene to Early Miocene in-sequence thrusting towards the European foreland. Foreland propagating thrusting is also regarded to be responsible for the progressive steepening of thrust units towards the internal parts of the fold-and-thrust-belt, which causes overturning of the innermost flysch units and the PKB.
Crosscutting relationships observed in outcrops give evidence that (N)NW-directed shortening is followed by ENE-striking strike-slip faulting (DF2), reactivating former thrusts of DF1. Strike-slip faults occur at the front of and within the Bystrica and Biele Karpaty Unit close to the PKB. Structures of DF1 and DF2 are further cut or overprinted by (N)NE-striking sinistral strike-slip faults and fold-thrust structures related to (N)NE-directed shortening (DF3). Structural data and geological maps indicate that (N)NE-striking strike-slip faults and NNEdirected out-of-sequence thrusts coincide with bends at the front of the Magura and Bystrica Unit.
Structures from the NW margin of the adjacent PKB prove a complex polyphase deformation history. Multiple folding events, tilted and refolded ramp-flat structures and overturning of strata complicate deciphering individual deformation events and their relative chronology. However, NNW-directed shortening, which postdates large scale overturning of strata, was identified in the region around the Middle Váh Valley. There, the NNW-directed shortening is followed by NNE directed shortening. Deformation styles are comparable with DF1 and DF3 in the flysch units. NNW-directed shortening is interpreted as out of sequence thrusting during deformation DF1. In addition, ENE-striking sinistral strike-slip faults are recorded within the PKB, close to the border to the Biele Karpaty and Bystrica Unit.
The outcrop-derived deformation history is compared to tectonics in the Vienna Basin area, where seismic data provide excellent constraints for deformation ages. In the Vienna Basin, out-of-sequence thrusting coeval with NE-striking sinistral strike-slip faulting occurs in the flysch units and Northern Calcareous Alps during the Early Miocene contemporaneously with in-sequence thrusting in the external Waschberg Unit. Early Miocene NE-striking sinistral strike-slip faults are cut by (N)NE-striking Middle to Late Miocene sinistral strike-slip faults. NE- and (N)NE-striking strike-slip faults mapped in the Vienna Basin are related to the eastward lateral extrusion of the Eastern Alps towards the Pannonian region, whereas (N)NE-striking faults are linked to the pull-apart stage of the Vienna Basin during Middle to Late Miocene times. DF2 and DF3, identified in the Outer West Carpathians are therefore interpreted as to be linked to Miocene extrusion kinematics. ENE-striking strike-slip faulting (DF2) may represent Early Miocene kinematics. NNE-directed out-of-sequence thrusting and (N)NE-striking strike-slip faults (DF3) are interpreted to be linked to the pull-apart stage of the Vienna Basin. Considering several blocks moving towards (N)NE at different velocities during Miocene lateral extrusion, structures of DF3 may depict a transfer of such (N)NE-directed movements to thrusts into the Outer West Carpathians.